Grinding machine



R. G. HATSTAT ETAL 3,534,509

GRINDING MACHINE Oct. 20, 1970 Original Filed April 28, 1965 3 Sheets-Sheet l .\H"Yl I? =z 7 MM$QL2F F 4? I 45 43 m 46 FIG. 2

ROBERT G. HATSTAT ROBERT T; WESTON INVENTOR.

wLA/tmgv Oct. 20, 1970 R. e. HATSTAT ETAL 3,

GRINDING MACHINE Original Filed April 28, 1965 3 Sheets-Sheet 2 FIG. '3

FIG. 5

ROBERT G. HATSTAT ROBERT 7'. WESTON GRINDING CYCLE .INVENTOR.

Oc tQZO, 1970 R. 5. HATSTAT ETAL 3,534,509

GRINDING MACHINE Original Filed April 28, 1965 3 Sheets-Sheet 5 FIG. 4

95 ROBERT s. HATSTAT ROBERT T. WESTON 1N VENTOR.

United States Fatent O 3,534,509 GRINDING MACHINE Robert G. Hatstat, Rutland, and Robert T. Weston,

Holden, Mass., assignors to The Heald Machine Company, Worcester, Mass., a corporation of Delaware Continuation of application Ser. No. 451,552, Apr. 28,

1965. This application Jan. 16, 1969, Ser. No. 805,076

Int. Cl. B24b 49/00 US. Cl. 51-165 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a grinding machine and, more particularly, to apparatus for generataing a surface of revolution by the abrasion process which uses the controlled-force principle during a roughing grind and uses the feed-rate principle during a finish grind.

This application is a continuation of our application Ser. No. 451,552, filed Apr. 28, 1965, now abandoned.

In the operation of grinding machines, there are two systems for feeding the rotating abrasive wheel into the workpiece surface. Under one system, the rate of feed is controlled and the force may vary in an indeterminate manner. Under the other system, the force is maintained at a predetermined value or in accordance with a particular pattern, so that the rate of movement of the wheel into the workpiece varies. Under some conditions, neither of these methods is entirely satisfactory. With the controlled force system, vibrations can take place because the system is usually carried out with a friction-free slide and with a hydraulic actuator for producing the force. On the other hand, under the feed rate type of operation, it is diflicult to operate at an optimum rate of stock removal and the finish is apt to be relatively poor. Nevertheless, with the feed rate system, vibrations are not so much of a problem, since the feed usually takes place by means of a solid screw while, with controlled force, it is possible to obtain the maximum rate of stock removal commensurate with the structure of the wheel and the material of the workpiece. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine which is capable of maximum rate of stock removal without difliculty due to vibration.

Another object of this invention is the provision of a grinding machine capable of providing a cycle having the advantages of controlled force grinding and of feed rate grinding.

A further object of the present invention is the provision of a grinding machine incorporating a cycle under which the major stock removal takes place under the controlled force system, while finishing takes place under a feed rate system.

It is another object of the instant invention to provide a grinding machine giving an optimum rate of stock removal with excellent finish and sizing.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its strucural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a plan view of a grinding machine embodying the principles of the present invention,

FIG. 2 is a front elevational view of the machine with portions removed,

FIG. 3 is a vertical sectional view of the machine taken on the line IIIIII of FIG. 2,

FIG. 4 is a schematic view of hydraulic circuitry used in the machine, and

FIG. 5 is a graphical representation of the grinding cycle used in the machine.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the grinding machine is shown as consisting of a base 11 having a flat horizontal upper surface on which are mounted a workhead 12 and a wheehead 13. The workhead is carried on a workhead table 14 which is mounted for longitudinal motion on the base 11 by means of ways 15. Similarly, the wheelhead 13 is carried on a wheelhead table 16 which is mounted for transverse sliding motion on the base 11 by means of ways 17. Extending between the workhead table 16 and the base 11 is a feed cylinder 18 which is suitably provided with fluid pressure to bring about movement of the table 16 transversely of the base. Similarly, a hydraulic cylinder 19 connects the table 14 to the base 11 and brings about longitudinal movement of the table 14 over the ways 15.

Extending from the wheelhead 13 is a rotatable spindle 21 carrying on its outer end an abrasive wheel 22. Carried by the workhead 12 and rotated thereby is a workpiece 23; for the purpose of illustration, this workpiece is shown as the race of a ball bearing. The inner bore is being ground by the abrasive wheel 22 and the workpiece is supported on its outer cylindrical surface. Residing in the bore of the workpiece during the grinding operation is a pneumatic air gage 24 of the well-known type which gage is connected to a control box 25. The control box 25 provides a flow of air to the gage 24 in a well-known manner. The amount of air that is able to pass between the surface of the gage and the surface of the bore of the workpiece is an indication of the workpiece size and this flow is transmitted to the control box 25 which contains various pressure switches to operate electrically to open and close solenoid valves in the hydraulic circuitry of the machine.

Slidable on the upper surface of the base 11 is a block 26 which, at its rearward end, is threadedly attached to a threaded shaft 27 which, in turn, is driven by a motor 28 fastened to the base 11. This motor is of the type capable of small discrete rotary increments in response to pulses received from an electrical control. By regulating the nature and number of the pulses from the electrical control, it is possible to rotate the motor quickly or slowly in exact amounts to make the block 26 move transversely over the surface of the base 11. In the present apparatus, this motor is used to produce compensation after dress and to provide for retraction of the wheel at a suitable time of the grinding cycle, as is well known. A dressing diamond 29 is mounted on the workhead table 14 in position to engage the wheel 22 during a dressing traverse at a suitable time in the grinding cycle.

The block 26 is provided with a transverse slot 31 and in this slot resides a horn 32 extending downwardly from the undersurface of the wheelhead table 16. The front of the block 26 is provided with a hardened metal insert 33-. Mounted on the front portion of the wheelhead table 16 is a retractable stop 34 having a contact rod 35 extending toward the block 26 and toward the metal insert 33. Mounted at the front of the retractable stop is a gear 36 and to the right (in FIG. 2) is an adjusting knob 37.

Referring now to FIG. 2, it can be seen that the gear 36 is attached to the outboard end of the rod 35 and that the gear is contacted by a feed-back mechanism 38. This feed-back mechanism consists of a housing 39 having a bore 41 in one end of which is slidably carried a piston 42. A conduit 43 is connected to the extreme end. Similarly, the other end of the housing is provided with a bore 44 carrying a piston 45, the bore being connected to a conduit 46. Connected to the pistons 42 and 45 are pawls 47 and 48, respectively, ar ranged to contact the ratchet wheel or gear 36 on occasion. A spring-loaded plunger 49 is mounted in the housing 39 and engages the teeth of the gear to prevent rotation by vibration.

Forming part of the retractable stop 34 is a housing 51 through which extends a bore 52 slidably carrying a piston 53. Connected through the housing to the left end of the bore 52 is a conduit 54. Also connected to the housing is a conduit 55 connected into a passage leading through an adjustable throttle 56 (which is controlled by the knob 37) to the right-hand end of the bore 52. As can be seen in FIG. 3, a check valve 57 is connected around the throttle 56.

As is evident in FIG. 3, extending rearwardly from the center portion of the piston 53 is a rod 58. This rod is pivotally mounted in the top of a crank arm 59 whose other end is connected through a sleeve 65 to the contact rod 35. The forward end of the slot 31 in the block 26 is provided with a hardened metal button 61 adapted to engage, on occasion, a similar hardened metal button 62 located on the forward surface of the horn 32. In that view, it can be seen that the feed-back mechanism 38 is mounted on the underside of the housing 51 of the retractable stop 34 by means of a bracket 63.

In FIG. 3, it can also be seen that the contact rod 35 is made up of a central shaft 64 mounted in a sleeve 65 and locked against rotation relative thereto. At its outboard end, the sleeve is provided with a threaded portion 66 which threadedly engages the interior threaded bore of a nut 67. The exterior is also threaded and is threadedly engaged in the interior of a threaded bore in the housing 51. The nut 67 is also bolted to the ratchet wheel or gear 36. The sleeve 65 is surrounded by a larger sleeve 68 located inwardly of the threaded portion 66. Between the inner surface of the sleeve 68 and the outer surface of the sleeve 65 are located a number of small bearing balls 69. Furthermore, pressure oil is provided in this same space through a passage 71 extending through the sleeve 68. This hydraulic pressure operates to bias the sleeve 65 rearwardly at all times and acts as a piston to take up all backlash between the threaded engagements with the nut 67.

As is evident in FIG. 2, the crank arm 59 is provided with a laterally-extending finger 72 having a hardened metal button 73 adapted to contact an adjustable vertical stop shaft 74. The stop shaft is mounted in the housing of the retractable stop 34 and is provided with a threaded engagement therewith for vertical movement. A knob 75 located at the upper portion provides for its adjustment.

Referring now to FIG. 4, which shows the hydraulic circuitry in the machine, the oil for the circuitry is provided by a pump 76 driven by a motor 77. The pump is connected to a line 78 adapted to carry 500 p.s.i. unfiltered oil. The pump is also connected through a filter 79 to a line 81 adapted to carry a 500 p.s.i. filtered oil. The pump is also connected through a pressure regulating valve 82 which provides filtered oil at 125 p.s.i. to a line 83. Extending through the circuitry is a p.s.i. drain line 84 and a main drain line 85. The pressure lines 78, 81, and 83 operate with the drain lines 84 and 85 to regulate various cylinders in the machine, including the workhead table cylinder 19 which has been described in connection with FIG. 1. Also included in the circuitry is a TABLE IN dashpot 86, a TABLE OUT dashpot 87, a LOADING cylinder 88, the FEED cylinder 18 (which has also been described in connection with FIG. 1), a RETRACTABLE STOP PRE- LOAD cylinder 89, a WHEELHEAD SWIVEL cylinder 91, the GAGE IN cylinder 92, another GAGE IN cylinder 93, and DIAMOND TURNER cylinders 94 and 95. Regulating the flow of pressure fluid from the pressure lines 78, 81, and 83 to these cylinders and to the drain lines 84 and are the following solenoid valves:

TABLE INDEX valve 96, a speed valve 97, a load valve 98, a FEED AND RETRACT valve 99, a pressure-regulating valve 101 for producing low pressure fluid and a pressure-regulating valve 102 for producing high-pressure fluid, the HIGH-LOW FORCE CROSS-SLIDE valve 103, a CROSS-SLIDE FEED valve 104, a BACK-OFF valve 105, a DAMPER BY-PASS valve 106, as well as WHEELHEAD SWIVEL valve 107, the SINGLE-JET GAGE valve 108, the DOUBLE-JET GAGE valve 109, a DIAMOND TURNER valve 111, a FEED-BACK valve 112, and another FEED-BACK valve 113. It can be seen that the valves 112 and 113 are conected to the conduits 43 and 46 leading to the feed-back mechanism 38. Associated with the piston 53 and its bore 52 is the throttle 56 and the check valve 57.

The operation of the apparatus will now be readily understood in view of the above description. A typical cycle takes the general form shown in FIG. 5 wherein the abscissa represents the passage of time and the ordinant is the location of the surface of the abrasive wheel 22 relative to the axis of the workpiece 23. Starting at point a, the wheel advances to point b at low force rate. At the same time that this is taking place, the motor 28 is providing compensation for a distance y from the point b to a point 0 and is also advancing to overcome a previous retract movement by a distance x to a point a. The loading of a new workpiece, incidentally, has taken place before the point a, and the movement from the point a to the point b is on a rapid Transverse movement takes place under the impetus of head table 14 toward the wheelhead table 16 so that the wheel 22 lies within the bore of the workpiece 23. Transverse movement takes place under the impetus of the cylinder 18 on a rapid traverse movement. At the point d, the wheel contacts the workpiece 23 and grinding takes place at a low force rate from point d to a point e.

This low force is brought about by introduction of oil into the feed cylinder 18 originating in the pressure reducing valve 101 giving low pressure oil. The length of time that the low force grinding takes place is determined by a timer which is set off by the contact of the wheelhead table 16 with a limit switch (not shown) at point a which not only starts the low-force timer, but also energizes the low-force solenoid valve to connect the LOW-FORGE PRESSURE-REDUCING valve 101 with the cylinder 18. The amount of compensation y has been previously set into the machine and, of course, the retract amount has also been previously set into the machine controls. As soon as the low-force timer times out, it energizes a high-force solenoid and directs oil from the high pressure-reducing valve 102 to the cylinder 18 producing a high force grinding operation from the point e to a point f. At point 1 rod 35 contacts block 33 and feed valve 99 is energized to start feed cylinder to grind now at predetermined rate to first gage size. The gage 24 eventually determines that the grinding operation has progressed to the point where the workpiece bore has been enlarged to a first size. At that time, the gage control 25 operates a switch and this starts a spark-out timer and centers the feed valve 99'. No feed takes place, but the residual deflection in the spindle continues the grinding operation from the point 1 to the point g. This is done hydraulically by dump valve 104, back-off valve and damper bypass valve 106, to bring horn 32 up to contact button 62 against 61 to go from g to h. At that time, the cylinder 19 draws the workhead table 14- longitudinally causing the diamond 29 to pass over the surface of the wheel 27 along the line h to the point i. This is done by motor 28 drawing block 26 forwardly the amount of retraction. Then, the wheel moves on a traverse to bring the wheel into the bore of the workpiece and the wheel moves on rapid traverse from the point k to a point I without grinding any material. At this point, the inner end (referring to FIG. 3) of the control rod 35 contacts the hardened metal insert 33 on the block 26. The cylinder 18 presses the table rearwardly attempting to move the wheel into further contact with the workpiece. However, the table is unable to go any further because of the retractable stop 34 and its contact rod 35. At that time, the valve 99 is actuated by the electrical controls of the machine so that oil is presented to the piston 53 and the bore 52 which acts as a feed cylinder. The cylinder moves to the right in FIG. 2 carrying the crankarm 59 with it which, because of the engagement of the threaded portion 66 of the sleeve 65, causes the control rod 64 to move outwardly (to the right), thus permitting the wheelhead table 16 to move rearwardly and move the wheel into the workpiece on a grinding operation. This continues from the point I to the point m for a feed rate grinding operation. The gage 24 indicates when the workpiece has come close to finish size and stops the operation of the piston 53 at the point In. From then on, grinding takes place from the point In to the point n on a spark-out operation. The gage 24 indicates the final size at the point 12 and orders the wheel to retract from the point n to the point 0. It should be noted that the axis of the wheel at that point 0 has been moved inwardly the distance from the point a to the point 0, or the distance, y, which compensates for the amount taken off during the dressing part of the cycle. The wheel, of course, moves out of the workpiece bore in order to change workpieces.

During the feed rate grinding from point I to point m, high pressure oil originating in the high-pressure reducing valve 102 is admitted to the cylinder 18 so that the contact rod 35 presses tightly against the block 26. At the point In, a spark-out timer measures the time it takes before the gage indicates that final size has been reached at the point 11. If this consumes either too great or too little an amount of time, this fact is indicated to the reset solenoids 112 and 113 which present oil to the feed-back mechanism 38 to operate the pawls 47 and 48 and rotate the gear 36 in one direction or the other. This compensates for long-term variations of the sizes of workpieces. Such a change in size may take place for various reasons, among which are thermal changes in the body of the grinding machine.

It can be seen, then, that all of the advantages of both the controlled force and the feed rate method of grinding are used in this present apparatus. Grinding takes place at a very high rate from the point e to the point 1, rounding up previously having taken place under a low-force grinding from the point d to the point 2. Nevertheless, in the finish portion of the cycle from the point I to the point It grinding takes place with a positive screw feed, thus giving a rigid Wheel support which prevents vibration or tendency for the wheel to duplicate irregularities or any out-of-round condition in the surface of the workpiece.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A grinding machine for finishing a surface of revolution of a workpiece, comprising (a) a base,

(b) a workhead mounted on the base and adapted to support the workpiece and to rotate it about the axis of the said surface,

(c) a wheelhead mounted on the base and adapted to support and to rotate an abrasive wheel,

(d) an actuator connecting the wheelhead and the workhead for bringing about relative movement therebetween to bring about operative engagement between the wheel and the workpiece surface with a predetermined force during a roughing grind,

(e) a stop overriding the said actuator at times and regulating the rate of relative movement between the workhead and the wheelhead during a finished grind, and

(f) means for regulating pressure in the actuator to cause the wheel to contact the workpiece with a low force at the first part of the roughing grind and with a high force at the second part of the roughing grind.

2. A grinding machine for finishing a surface of revolution of a workpiece, comprising (a) a base,

(b) a workhead mounted on the base and adapted to support the workpiece and to rotate it about the axis of the said surface,

(c) a wheelhead mounted on the base and adapted to support and to rotate an abrasive wheel,

(d) an actuator connecting the wheelhead and the workhead for bringing about relative movement therebetween to bring about operative engagement between the wheel and the workpiece surface with a predetermined force during a roughing grind, and

(e) a stop overriding the said actuator at times and regulating the rate of relative movement between the workhead and the wheelhead during a finish grind, the stop engaging the wheelhead and being rotatable for advancing and retracting by means of an actuator.

3. A grinding machine as recited in claim 2, wherein a feedback actuator engages the stop for rotation to compensate for the variation in size of successive workpieces away from a predetermined size.

4. A grinding machine as recited in claim 3, wherein the feedback actuator consists of opposed hydraulic cylinders having pawls which selectively engage a ratchet wheel mounted on the stop for the rotation thereof.

5. A grinding machine as recited in claim 2, wherein pressure fluid is introduced into the stop to bias the engagement with the wheelhead to reduce backlash.

References Cited UNITED STATES PATENTS 2,119,296 5/1938 Schmidt 51-95 2,241,634 5/1941 Decker 51165 X 2,243,405 5/1941 Wine.

2,367,759 1/1945 Decker et a1 5l-2 X 2,647,348 8/1953 Hahn 51-165 2,897,638 8/1959 Maker 51-165 OTHER REFERENCES Heald advertisement, Machinery, December 1955; back of front cover of magazine.

LESTER M. SWINGLE, Primary Examiner 

